1. Field of the Invention
The present invention relates to a redundant structure in an optical wavelength multiplexing system.
2. Description of the Related Art
With the increase in the processing speed and the capacity of information, the need for broadening the band of/increasing the capacity of a network and a transmission system has been required. Therefore, as one of the means of realizing this, the configuration of an optical network based on a wavelength division multiplexing technology has been desired. When configuring an optical network, a key point is an optical path cross connection system in an optical wavelength multiplexing system (a device for routing optical signals inputted from a plurality of optical fibers, whose wavelengths have been multiplexed, to desired output optical fibers for each wavelength).
On the other hand, with the increase in a transmission capacity, faults which occur in the transmission line and a node have a great influence. Therefore, it is necessary to provide a redundant configuration in the transmission line and the node in order to increase the reliability at the time of faults.
FIGS. 1A and 1B show examples of a redundant configuration in a conventional optical wavelength multiplexing system.
FIG. 1A shows an example of a redundant configuration of a node output portion in the conventional optical wavelength multiplexing system (for example, optical path cross connection system; optical XC system).
A node is duplexed (0-system/1-system), and is provided with optical selectors 2700 and 2701 at the output. Monitor circuits 2702 and 2703 detect whether output optical signals are normal or abnormal for all the wavelengths outputted from each node, and control the switching of protection switches (optical selectors 2700 and 2701).
In FIG. 1A, a set of an optical XC node, a protection switch, and monitor circuits 2702 and 2703 is provided. Actually, however, the same number of optical selectors and the same number of monitor circuits are provided as that of a 0-system line 2704 and a 1-system line 2705, outputted from the optical XC nodes.
The monitor circuits 2702 and 2703 input both the 0-system line 2704 and the 1-system line 2705, which correspond to the optical XC node (0) and the optical XC node (1), respectively. Then, the circuits receive optical signals, and monitor whether or not faults occur on the lines. When the 0-system line is being used, if the monitor circuit 2702 or 2703 detects the occurrence of a fault in this 0-system line, the optical selector 2700 or the optical selector 2701 is controlled to switch to the 1-system line.
FIG. 1B shows an example of a redundant configuration in an input transmission line to a node in a conventional optical XC system.
The transmission line is duplexed (0-system/1-system), and a protection switch 2708 is provided at the preceding stage of the optical XC system. The protection switch 2708 is composed of optical selectors 2709 and 2710, and monitor circuits 2706 and 2707 corresponding to these optical selectors. The optical transmission line which has redundancy to provide a 0-system and a 1-system is configured by a set of a 0-system transmission line and a 1-system transmission line, and this set of transmission lines is connected to the optical selector 2709 or 2710. The monitor circuits 2706 and 2707 detect whether the input optical signals from each transmission line are normal or abnormal for all the wavelengths. When a fault is detected in the optical signals, the protection switch 2708 is controlled to be switched. In the case of FIG. 1B, the optical XC node is not provided with a redundant configuration, but this node can further be provided with a 0-system node and a 1-system node as shown in FIG. 1A. In this case, the optical selectors 2709 and 2710 should be provided with two inputs and two outputs.
FIGS. 2A and 2B show examples of the configuration of a conventional protection switch (optical selector). FIG. 2A shows the case where an optical selector is configured by 2xc3x972 optical switches. When a transmission line to be inputted to the optical selector has redundancy to provide a 0-system and a 1-system as shown in FIG. 1A or 1B, only one output is used.
FIG. 2B shows a configuration where gate-type optical switches and an optical coupler are combined.
These switches are basically the same as a conventionally known optical switch, but they make use of a function of switching the optical path of the inputted optical signal. That is, these optical switches are configured in such a way that the optical signal whose optical path has been switched is prevented from being externally outputted by using a photo absorption material or the like, which is provided along the optical path. The optical switches having such a configuration are used as optical gates. An optical coupler can be a conventionally-known optical coupler, and only transmit the optical signal outputted from the optical gate to the transmission line.
As an example of such an optical switch, an optical switch which is composed of an inductive material such as LiNbO3 or a semiconductor such as InP, GaAs or the like, can be adopted. This switch performs ON/OFF control by being applied by a voltage or a current. As one example of the details of such an optical switch, please refer to the document xe2x80x9cIEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 6, NO. 7, pp. 1267-1272 (1988)xe2x80x9d or the like. 
According to the conventional configuration, one wavelength transmission system is used. Accordingly, when a monitor circuit detects a fault only in one wavelength of an optical signal having a plurality of wavelengths which have been multiplexed, even the remaining normal optical signals are simultaneously switched to the other system by a protection switch.
In the case of one wavelength transmission, since the optical signal to be transmitted has one wavelength, that is, one channel, no problem will arise. In an optical wavelength multiplexing system, however, since an optical signal of a plurality of wavelengths is transmitted to one transmission line, even optical signals in which faults do not occur are also switched.
Therefore, in an originally normal optical signal, a signal disconnection is generated at the time of the switching so that the transmission efficiency will deteriorate. Even if an optical switch which performs processings at high speed up to a level where any error will not occur in directing a signal, a circuit is required for matching a phase of an optical signal of the 0-system with that of the 1-system before the protection switch. The same number of these circuits is required as that of the wavelengths so that the amount of hardware will increase. Further, it is more difficult to perform the switching and the phase matching for a high speed optical switch, as the transmission speed increases.
In spite of the above-mentioned problems, however, no specific configuration other than a configuration of one wavelength transmission is proposed at present, for the redundant configuration of an optical wavelength multiplexing system.
The present invention provides an optical wavelength multiplexing system having a redundant configuration only for switching the optical signal of a wavelength in which a fault occurs, among optical signals whose wavelengths have been multiplexed.
In the optical wavelength multiplexing system according to a first aspect of the present invention, a plurality of input and output optical fibers transmitting wavelength-multiplexed optical signals are included. Further, in this optical wavelength multiplexing system for processing the optical signals for each wavelength, a protection switch is provided on an output side of a node duplexed into a first system and a second system. This protection switch comprises a demultiplexer for demultiplexing an optical signal to be inputted after its wavelengths have been multiplexed, into optical signals for each wavelength; an optical selector provided for each wavelength, for selecting optical signals outputted from either one of the duplexed nodes; and a multiplexer for coupling optical signals for each wavelength transmitted from the optical selector, is provided. When a fault is detected in an optical signal of a certain wavelength included in optical signals transmitted from either one of systems, the optical selector only switches an optical signal of the wavelength in which the fault is detected, into the other system.
An optical wavelength multiplexing system according to a second aspect of the present invention, includes a plurality of input and output optical fibers transmitting wavelength-multiplexed optical signals. In this optical wavelength multiplexing system for processing optical signals in units of wavelengths, a protection switch is provided on an output side of a node which is duplexed into a first system and a second system. This protection switch comprises an optical selector provided for each wavelength, for selecting optical signals outputted from either one of the duplexed nodes, and a multiplexer for coupling optical signals for each wavelength transmitted from the optical selector. When a fault is detected in an optical signal of a certain wavelength included in optical signals transmitted from either one of the systems, the optical selector only switches an optical signal of the wavelength in which the fault is detected, into the other system.
An optical wavelength multiplexing system according to a third aspect of the present invention, includes a plurality of input and output optical fibers transmitting wavelength-multiplexed optical signals. In this optical wavelength multiplexing system for processing optical signals in units of wavelengths, a protection switch is provided on a transmission line which is duplexed into a first system and a second system. This protection switch comprises a multiplexer for multiplexing optical signals to be inputted after their wavelengths have been multiplexed, into optical signals for each wavelength; an optical selector provided for each wavelength, for selecting optical signals outputted from either one of the duplexed nodes, and a multiplexer for coupling optical signals for each wavelength transmitted from the optical selector. When a fault is detected in an optical signal of a certain wavelength included in optical signals transmitted from either one of systems, the optical selector only switches an optical signal of the wavelength in which the fault is detected, into the other system.
An optical wavelength multiplexing system according to a fourth aspect of the present invention, includes a plurality of input and output optical fibers transmitting wavelength-multiplexed optical signals. In this optical wavelength multiplexing system for processing optical signals in units of wavelengths, a protection switch is provided on a transmission line which is duplexed into a first system and a second system. This protection switch comprises an optical selector provided for each wavelength, for selecting optical signals outputted from either one of the duplexed nodes, and a multiplexer for coupling optical signals for each wavelength transmitted from the optical selector. When a fault is detected in an optical signal of a certain wavelength included in optical signals transmitted from either one of systems, the optical selector only switches an optical signal of the wavelength in which the fault is detected, into the other system.
An optical wavelength multiplexing system according to a fifth aspect of the present invention, includes a plurality of input and output optical fibers transmitting wavelength-multiplexed optical signals. In this optical wavelength multiplexing system for processing optical signals in units of wavelengths, a filter for selecting an optical signal of a plurality of optional wavelengths is provided at a protection switch for switching the systems of the outputs of a node which has been duplexed into the first system and the second system. When a fault is detected in an optical signal of a certain wavelength included in optical signals transmitted from either one of systems, the optical selector only switches an optical signal of the wavelength in which the fault is detected, into the other system.
An optical wavelength multiplexing system according to a sixth aspect of the present invention, includes a plurality of input and output optical fibers transmitting wavelength-multiplexed optical signals. In this optical wavelength multiplexing system for processing optical signals in units of wavelengths, a filter for selecting a plurality of optional optical signals is provided at a protection switch for switching the systems of the output of a node which has been duplexed into the first system and the second system. When a fault is detected in an optical signal of a certain wavelength included in optical signals transmitted from either one of the systems, the optical selector only switches an optical signal of the wavelength in which the fault is detected, into the other system.
An optical wavelength multiplexing system according to a seventh aspect of the present invention, comprises a transmission line for propagating an optical signal, and a node connected to the transmission line, for propagating the optical signal. In this optical wavelength multiplexing system which has redundancy by providing transmission lines or nodes in plural, a monitor means and a switch means are provided. The monitor means monitors a wavelength-multiplexed optical signal to be transmitted, for each wavelength. The switch means only switches an optical signal of a wavelength in which a fault occurs, to an optical signal transmitted from the other corresponding transmission line or node, among optical signals transmitted from the plurality of the transmission lines or nodes.
When a fault is detected in an optical signal of a certain wavelength among optical signals whose wavelengths have been multiplexed to be transmitted, the present invention only switches the system of the optical signal of a wavelength in which a fault occurs, but does not switch all the optical signals whose wavelengths have been multiplexed, to any one of the systems provided in plural. Therefore, the present invention does not switch the system of optical signal in which a fault does not occur, so that a transmission deterioration such as a signal disconnection caused by the switching of the system of a normal optical signal will not be generated.